Originally from a military family, Li was made a jinshi (the highest scholar-official title in imperial China) in 1598. In 1601 he met the Italian Jesuit Matteo Ricci, who was one of the first Westerners allowed into the interior of China. To gain acceptance, Ricci had first learned the Chinese language and culture, which in turn enabled him to spread knowledge of Western science and religion. Li was greatly attracted by Ricci’s teachings, although he only consented to be baptized by him in 1610, shortly before Ricci’s death. Li was regarded as one of the most important Christian converts in the late Ming dynasty Roman Catholic mission.

Li began his collaboration with the Jesuits by engraving and printing numerous copies of Ricci’s world map, which altered many Chinese views of world geography. The German Jesuit Christopher Clavius (best known for the Gregorian calendar) had been Ricci’s teacher and, together with Li, Ricci translated his arithmetic primer Epitome arithmeticae practicae (1585; “Selected Arithmetic Methods”) as Tongwen suanzhi (1614). This book systematically introduced European-style mathematical notation, while Li included complementary elements from traditional Chinese mathematics. Li also wrote a short treatise on geometry dictated by Ricci. Together with the Portuguese Jesuit Francisco Furtado (1589–1653), Li also translated Commentarii Collegii Conimbricensis e Societate Iesu: In Universam Dialecticam Aristotelis Stagiritæ (“The exploration of the patterns of names”). Based on Aristotle’s On the Heavens (4th century bc), this book was originally used as a textbook at the College of Coimbra in Portugal. In addition, Li translated European logic treatises. He also brought together and published a series of books composed by the Jesuits with Chinese help, Tianxue chuhan (1629; “First Collection of Writings on Heavenly Learning”), that included 20 Western scientific and religious titles. In 1629 he was recommended by Xu Guangqi to work at the Imperial Astronomical Bureau on Chongzhen lishu (1628–44; “Astronomical Treatises of the Chongzhen reign”), a compilation of European mathematical and astronomical books.